The technology of hollow light guiding tubes based on optical prisms and polished planar surfaces, U.S. Pat. No. 4,260,220, is in practice, marginally efficient and limited in its commercial applications. The production, in volume, of micro-prism optical light film by replicating a myriad of optical prisms on one side and a polished surface on the other, and made of thin, flexible, transparent polymeric material by 3M Company, St. Paul, Minn. generated the impetus which brought about the development of optical prism light guiding tubes into optical prism light-distributing tubes, which if efficient and cost effective, could have commercial significance. A representative sampling of the presently evolved state of the art for optical prism light-distributing tubes using prism optical light film is shown in the following sample of U.S. Pat. Nos.: 4,542,449; 4,615,579; 4,750,798; 4,787,708; 4,791,540; 4,805,984; 4,834,495; 4,850,665; 5,475,785; and 5,483,119.
The present invention is based on the premise that prism controlled light-guidance and prism controlled light-distribution in the same tube at the same time are antithetical functions which simply get into each other's way at the cost of efficiency. Thus, the merger of simple light-guidance by tubes using prismatic optical light film into a new and more complex art of light-distribution by tubes also using the prismatic film was an illogical, if not costly mistake for those enticed into the field. This, coupled with the facts that optical light film: (i) cannot guide light beams having angles of incidence over 27.6 to 29.5 degrees; (ii) cannot distribute light beams having angles of incidence less than 27.6 to 29.5 degrees; (iii) is delicate to handle and easily damaged, even by a casual finger print; (iv) cannot be curved into small radii, (v) degrades, in its preferred polycarbonate form, in the presence of ultra violet light; (vi) becomes dysfunctional in the presence of moisture and dust; and (vii) is, at least at this point in time, disproportionately expensive relative to the sum of all other components of which the tube is constructed, all invite other and better solutions than prismatic optical light film to the problem of distributing light from a concentrated source by means of long tubes.
It is therefore an object of the present invention to provide efficient light-distributing tubes which do not require in any way the optics of prismatic film.
It is another object of the invention to provide light-distributing tubes which include a light redirecting structure within the tube which can nevertheless be fabricated in a flat, substantially void-free configuration for inexpensive handling and shipping, but which can be easily converted in situ to its fully operative configuration.
It is another object of the invention to provide efficient, inexpensive, durable, environmentally stable light-distributing tubes.
It is another object of the invention to provide a light-distributing tube which can distribute most of the light injected into the tube on the first pass of the light down the tube.